Process for treatment of wood pulp by percolation



Aug. 18, 1931. I E. MORTERUD 5 PROCESS FOR TREATMENT OF WOOD PULP BYPERCOLATION Filed Nov. 10, 1950 lll lli'll Patented Aug. 18, 1931 UNITEDSTATES EINAR MORTERUD, OF TORDEROD, NEAR MOSS, NORWAY PROCESS FORTREATMENT OF WOOD PULP BY PERCOLATION Application filed In wood pulpdigesters it is well known to circulate liquor or washing liquid throughthe digester for the purpose of dissolving the chemical compounds whichare to be removed from the pulp or for washing away the remains of theliquor after the digesting process has been terminated.

According to the process which has been in use for this purpose thepercolating liquid is allowed to pass in a continuous flow through thewood pulp to be digested or washed.

In accordance with the present invention the supply of percolatingliquid to the top of the digester takes place with interruptions so asto cause an intermittent flow of liquid through the wood pulp to betreated.

Thereby a kind of pulsation is caused to take place in the material tobe treated, as the latter will be exposed to a pressure each time anamount of li uid is supplied to the top of the digester an to a decreaseof pressure when the particular quantity of liquid has passed.

The process is particularly adapted for the purpose of washing digestedpulp, but may also with advantage be utilized in connection with thedigesting process proper.

As it will be understood the comression above referred to of the wetpulp wil cause a certain amount of liquid to be pressed out of the same,and this expelled liquid will be car ried along with the percolatingliquid.

After the particular amount of liquid has passed the fibres will againexpand so as to absorb an amount of -fresh liquid every time an amountof liquid passes through the pulp.

The variation of pressure caused by the intermittently suppliedpercolating liquid may be further accentuated by means of as pressure inthe digester, said gas pressure eing supplied every time a quantity ofpercolating liquid is being introduced, the pressure being againrelieved after the particular 5 quantity of liquid has passed. The saidpressure relief may be carried so far as to cause a boiling of theliquid absorbed by thepulp, which has the efiect of giving a moreefiicient digestion. In case the treatment takes place at a temperatureabove the boiling point of November 10, 193( Serial No. 494,756, and inNorway November 20, 1929.

the liquid the said pressure release may be caused simply by letting outsteam.

Another effect which tends to increase the efficiency of the treatmentis the higher velocity with which the liquid is now passing the pulpparticles, whereby liquid to take adhering particles of old away isincreased.

'It has also been found that when the percolating liquid is suppliedintermittently in separate quantities and in accordance with the presentprocess, the percolating liquid is less liable to form paths through thepulp to be digested, and all parts of the liquid supplied to the top ofthe digester will pass through the digester on approximately verticalpaths.

Further, according to the present process it is possible to graduallyincrease the speliquid cific weight of the liquid supplied to thediester from each quantity to the next, for instance, by supplyingquantities of liquid with successively decreasing temperature, whichcannot be done in case of a continuous supply of liquid, as in that casethe liquid with higher specific weight will overtake and be mixed withthe other liquid in the digester.

If a single digester is used the process may be carried out by means ofthe arrangement illustrated on Fig. 1, where 1 is the digester, 2 thecirculating ump and 3 a collectin vessel provided with a siphon outlet4. when the liquid in the collecting vessel has reached a levelcorresponding to the highest point of the siphon outlet, the vessel willbe emptied by means of the siphon tube and a certain quantity of liquidis then supplied to the top of the digester through the distributingsieve 5. When the collecting vessel has been emptied as far as .to thelowest point of the siphon tube the current of liquid is interrupted ina known manner until the vessel has again been filled up to the toplevel. I

According to the-arrangement illustrated on Fig. 2 two digesters 1 and 6are provided, having their outlets connected with a common collectingtank 7. In this tank a pump 2 leads the circulating liquid to adistributing valve or cock 8, by means of which the current of liquidmay be conducted either to dithe ability of the caused automatically orby stance a top distributing sieve may be used,

which is divided into several concentric or sector shaped parts, and thecirculating liquid may be turned on to one section after the pjiiier bymeans of a distributing valve or the It is also feasible to use arotating distributing member, having approximately the form ofa sectorand by means of which the circulating liquid is successively conductedto the various parts of the surface area. of the digester. In that caseit will be understood that the-circulating liquid will take the form ofa helical layer of liquid moving axially throu h the digester.

Alt ough the process above described is particularly adapted for beingused in connection with digesting and washing of wood 821p, it will beunderstood that it may also utilized in connection with other materialswhich are to be treated by means of a current of liquid for extractingor washing pur ses.

C aims:

1. In a process for treating materials, such as wood pulp, with acurrent of liquid for the purpose of extracting, washing etc. supplyingthe liquid in such a manner to the vessel containing the material inquestion, that the liquid is caused to pass the various particles ofsaid material in an intermittent current.

said vessel and means for periodically interruptmg the connectionbetween the pressure side of said circulation pump and'the intake 1; tosaid vessel.

6. In an apparatus for carrying out the process according to claim 1 thecombination w1t h two or more vessels containing the materlal to betreated and a continuously operating circulation pump for supplyingliquid to the top of said vessels of means for alternately connectingsaid circulation pump with the several vessels.

In testimony whereof I afiix my signature.

EINAR MORTERUD.

2. In a process as claimed in claim 1 supplying quantities of liquid atdetermined intervals to the upper part of the vessel containing thematerial.

3. In a process as claimed in claim 1 exposing the material to anincrease of pressure simultaneously with each quantity of liquid and apressure decrease during each interval between two quantities of liquid.

4. In an apparatus for carrying out the process according to claim 1 thecombination with a vessel containing the material to be treated and acontinuously operating circulation pump of a collecting vessel forcirculating liquid separate from said first named vessel and connectedwith the latter as well as with the circulating pump.

5. In an apparatus for carrying out the process according to claim 1 thecombination with a vessel containing the material to be treated, acontinuously operating circulation pump for supplying liquid to the topof

